A theoretical study of acoustic cavitation produced by "positive-only" and "negative-only" pressure waves in relation to in vivo studies.

This study investigated the responses of gas bubbles in water, "viscous water" or "lung surfactant" exposed to "positive-only" or "negative-only" pressure pulses. The computational results obtained were compared to the in vivo experimental findings of Bailey et al. (1996), for the thresholds for, and extents of, biological damage endpoints in Drosophila larvae and mouse lungs exposed to similar pressure pulses. It is shown that, if cavitation were the mechanism responsible for these biologic effects, the two pulse types would be expected to produce very different thresholds and amounts of damage unless: 1. the bubbles involved were larger than the linear resonance radius, or 2. the cavitational activity were located within a fraction of a wavelength of an air-tissue interface. A noncavitational, acoustic force mechanism for the effects also is considered. Finally, it is suggested that the mechanical index may require modification when the focus of the acoustic field lies near an air-tissue interface.